Due to the development of wireless communication technology, more and more Ethernets are being used as an in-vehicle LAN. To enhance stable characteristics and reject higher common mode noise, a common mode filter has been widely adopted in in-vehicle LAN to negatively affect the effectiveness.
It is well known that a common mode filter is configured by two inductances magnetically coupled with each other and then inserted into the transmission line path to suppress common mode noise current.
FIG. 1 shows a first embodiment of the conventional common mode filter 1000. As shown in FIG. 1, the common mode filter 1000 includes a drum core 100, a first winding wires 10 and a second winding wires 20. In order to obtain two inductances magnetically coupled with each other, the first winding wires 10 and the second winding wires 20 are wound on the drum core 100 by the construction of single-layer pair of wires (SLPW). Both terminals of the first winding wires 10 and the second winding wires 20 are coupled with the electrode ends of the common mode filter 1000, respectively.
When a common current that includes some common noises passes through the common mode filter 1000, the same direction magnetically field will be induced in both winding wires 10 and 20. As a result, the inductive reactance of the first winding wires 10 and the second winding wires 20 will be increased. Furthermore, higher common independence characteristics will be presented in the common mode filter 1000 that is possible to selectively suppress and/or attenuate a common mode noise current.
The high common noise can be suppressed and/or attenuated in the disclosed the first embodiment of the conventional common mode filter 1000, however the first winding wires 10 and the second winding wires 20 are wound on said winding core 100 by single-layer pair of wires, this makes them costly, bulky and space-consuming. In other words, the impractical space utilization will result in the economic benefit being greatly downscaled.
FIG. 2 shows a second embodiment of the conventional common mode filter 2000. As shown in FIG. 2, the common mode filter 2000 includes a drum core 100, a first winding wires 10 and a second winding wires 20. In order to obtain two inductances magnetically coupled with each other, the first winding wires 10 and the second winding wires 20 are wound on the drum core 100 by the construction of double-layer pair with separate wires (DLPSW). Both terminals of the first winding wires 10 and the second winding wires 20 are coupled with the electrode of ends of the common mode filter 2000, respectively.
When a common current that includes some common noises passes through the common mode filter 2000, the same direction magnetically field will be induced in both winding wires 10 and 20. As a result, the inductive reactance of the first winding wires 10 and second winding wires 20 will be increased. Furthermore, higher common independence characteristics will be presented in the common mode filter 2000 that is possible to selectively suppress and/or attenuate a common mode noise current.
The high common noise can also be suppressed and/or attenuated in the disclosed second embodiment of the conventional common mode filter 1000. However, due to the first winding wires 10 and the second winding wires 20 are wound on said winding core 100 by double-layer structure, the existence capacitors of in high-frequency layers and the inherent functionality of parasitic capacitors in common mode filters with higher frequency characteristics results in the less attenuation of the common mode noise current.
FIG. 3 shows a third embodiment of the conventional common mode filter 3000. As shown in FIG. 3, the common mode filter 3000 includes a drum core 100, a first winding wires 10 and a second winding wires 20. In order to obtain two inductances magnetically coupled with each other, the first winding wires 10 and the second winding wires 20 are wound on the drum core 100 by the construction of double-layer pair of wires. Both terminals of the first winding wires 10 and the second winding wires 20 are coupled with the electrode of ends of the common mode filter 3000, respectively.
When a common current that includes some common noises passes through the common mode filter 3000, the same direction magnetically field will be induced in both winding wires 10 and 20. As a result, the inductive reactance of the first winding wires 10 and that second winding wires 20 will be increased. Furthermore, higher common independence characteristics will be presented in the common mode filter 3000 that is possible to selectively suppress and/or attenuate a common mode noise current.
Similarly, the high common noise can be suppressed and/or attenuated in the disclosed third embodiment of the conventional common mode filter 3000. However, due to the first winding wires 10 and the second winding wires 20 are wound on said winding core 100 by double-layer, the existence capacitors of in high-frequency layers and the inherent functionality of parasitic capacitors in common mode filters with higher frequency characteristics results in the less attenuation of the common mode noise current.
A variety of techniques can reduce and/or attenuate a common mode noise current. However, it is really the necessity, of implementing ways to reduce the cost drastically, shorten production time, and enhance the reproducibility of a common mode filter or layout design that must be considered addressing in the solution process.